Carboxylic acids correlation table

Ionization constants of czs-3-substituted acrylic acids have been correlated with the Hammett equation by Hogeveen (58) and by Charton (60). Charton has correlated ionization constants for a number of other c/s-vinylene sets with the Hammett equation (60). Charton and Charton have correlated some cw-vinylene sets with the extended Hammett equation [eq. (2)] (73). Sufficient data are available for twelve sets of cis-vinylene equilibria, of which four sets represent ionization constants of hydroxy compounds (sets 12-1 to 12-4) and eight sets represent ionization constants of carboxylic acids (sets 12-5 to 12-12). All sets have been correlated with eq. (24) and eq. (2). Sets studied are reported in Table XII. Results of the correlations are reported in Table XIII. Sets designated A were correlated with eq. (24), sets designated B were correlated with eq. (2). In the case of the second ionization constant of 2,3,5,6-tetrahydroxy-l,4-benzoquinone (set 12-3), it is uncertain which hydroxyl group ionizes therefore, the value for X = OH was excluded from the correlation. All of the sets 12-1 to 12-4 gave significant correlations with both eq. (24) and eq. (2),... 

To date, there have been four reports published that have examined the impact of 1,1-ADEQUATE correlation data on structure generation times and the number of structures generated for various CASE programs.46 47 53 55 The first of the studies discussed above used limited 1,1-ADEQUATE data in a COCON computation rim for the relatively simple molecule 4,5-dibromopyrrol-2-carboxylic acid (4).53 In the same report, the authors considered the effect of 1,1-ADEQUATE correlations that would theoretically be expected for manzacidin A (5), however no 1,1-ADEQUATE data were actually acquired. The results for 4 and 5 are summarized in Table 2. 

Since decarboxylation is a primary reaction of the aliphatic carboxylic acids, it is interesting to compare the radical yield measured at 77 K (3) with the yield of carbon monoxide plus carbon dioxide. These values are compared in Table III. The results suggest that there is a correlation between the loss of the carboxyl group and the formation of radicals in the carboxylic acids. 

Only a small number of substances have so far been investigated, and the available results are given in Table 2. These compounds should be more suitable than carboxylic acids for correlating acidity with inductive effects, since the negative charge is concentrated on one oxygen atom. 

The catalytic constants measured in 95% aqueous dioxan have been compared with piT-values in water. The twenty-four acids referred to in Table 3 are mainly carboxylic acids, but also include nitric acid, o-chloro-phenol and water. Two oximes show large positive deviations, and saccharin has considerably less catalytic activity than anticipated these substances have not been included in the correlation. A number of strong acids gave closely similar catalytic constants— HCl (3-05), HBr (2-30), CoHb.SOsH (2-30), MeSOsH (2-15), HCIO (1-25)—and the minor variations within this series are not in the expected order of acid strengths HCIO4 > HBr > HCl > ObHb. SO3H > MeSOsH. Presumably all these acids are converted in solution to the hydronium ion, the catalytic power of which is somewhat modified by ion-pairing with different anions in the solvent of low dielectric constant. The catalytic constants observed are consistent with the conventional value pJT = —1-74 for H36+. 

The data of Levitan and Barker ( ) on the ability of carboxylic acids to promote potassium ion conductance in mollusk neurons (Table III) was reexamined. One can write Equations 15 and 16 for simple benzoic acids, but salicylic acids do not give a good correlation in log alone (r = 0.785). 

Tseng and Ullman studied leaving groups such as tosyl, trityl, piperidyl, and substituted carboxylic acids. They found that the quantum yields for the elimination from 18 correlated directly with leaving ability of the p-substituent from the ground state (Table 1). 

Carboxylic acids The smallest carboxylic acid, formic acid, can be measured using infrared spectroscopy (Table 11.2), since it has characteristic absorption bands. As discussed earlier and seen in Fig. 11.33b, mass spectrometry with chemical ionization using SiF5 also revealed HCOOH in an indoor environment (Huey et al., 1998). However, since the sensitivity in these initial studies was about two orders of magnitude less than that for HN03, the detection limit may be about the same as that for FTIR and TDLS. Formic and acetic acids have been monitored continuously from aircraft (Chapman et al., 1995) and their surface flux determined by eddy correlation (Shaw et al., 1998) using atmospheric pressure ionization mass spectrometry. Detection limits are about 30 ppt. 

The remaining chemical classes such as alkene (R2 < 0.51), amine (R2 < 0.90), aromatic hydrocarbon (R2 < 0.29), carboxylic acid (R2 < 0.06), and sulfonic acid (R2 < 0.77) do not correlate well. Table 7.6 shows all the QSAR models using ELUMO as the molecular descriptor. 

The second condition which can permit a linear relationship between log P values is illustrated in the equations in Table III which relate the more lipophilic systems to octanol/water. For the isopentyl acetate and the nitrobenzene systems, the correlation with the octanol system is quite good with a single equation, but the only solute values available were those from a single homologous series (the carboxylic acids), and we predict that a wider selection of solutes would result in a poor correlation. 

The expected change in Bronsted exponent with change in reactivity is illustrated by the results [49] shown in Table 9 for the hydrolysis of vinyl ethers (mono alkoxy-activated olefins) which occurs by initial slow protonation of olefinic carbon as in mechanism (28). The value of R which is the catalytic coefficient for an acid of pK 4.0 calculated from results for carboxylic acids with pK around 4.0 is taken as a measure of the reactivity of the system. The correlation of a with reactivity is scattered but the trend is in the expected direction. The results are quite similar to those shown for the ionization of ketones in Table 2. For the proton transfers shown in Table 9 the Bronsted exponent has not reached the limiting value of zero or unity even when reaction in one direction is very strongly thermodynamically favourable. The rate coefficient in the favourable direction is probably well below the diffusion limit, although this cannot be checked for the vinyl ethers. Non-limiting values for the Bronsted exponent have also been measured in the hydrolysis of other vinyl ethers [176]. 

Dimroth et al. introduced 8 as a solvatochromic probe of solvent polarity having absorption in the visible region it shows the largest solvatochromic shift of any substance yet reported. (30) is calculated with Eq. (8-76), like Z. (The peculiar symbolism arose because compound 8 happened to be No. 30 on the list of substances studied by Dimroth et al.) The shift is hypsochromic as solvent polarity is increased. Table 8-16 gives some t (30) values. - E (30) is linearly correlated with Z. and this correlation allows Ex (30) values to be indirectly estimated for carboxylic acid solvents, which protonate the phenolic oxygen of 8. A secondary solvatochromic probe is also required for hydrocarbon solvents, in which 8 is not soluble. 

Buccal Absorption of Acids. When a data set contains high log D values, quadratic terms in log D enter in to regression analyses just as with high log P s. Beckett and Moffat (6) measured the buccal absorption rates for a range of carboxylic acids (Table III). Again we find the rates are correlated well with an equation in log D terms alone (eq 7). An optimum log D of 3.28 can be calculated. The best alternative analysis is eq 8 7). 

The cr value alone can, of course, be used to understand the mechanism of those reactions which do not come under the ambit of cj+ and u values. For instance, the base hydrolysis of a benzoic acid ester may take two different pathways (a) nucleophilic attack of hydroxide ion on the carbonyl carbon to result in a tetrahedral intermediate, in a rate determining step, followed by its collapse into carboxylic acid or (b) nucleophilic attack of hydroxide ion on the alkyl carbon of the ester function, leading to the formation of the carboxylate directly. Since the carbonyl carbon is closest to the ring, the effect of a substituent felt by it must be much larger than the effect felt by the alkyl carbon. Hence, the rate of hydrolysis will be expected to increase much more in the former instance than in the latter with the increase in the substituent s a value. This is indeed the case as evident from the a versus rate constant k given in Table 3. The large increase in the rate of hydrolysis with the increase in cr could be justified only if the tetrahedral pathway is involved. The correlation of cr with log k is linear as seen from the plot in Fig. 5. 

Group IV (Types VIA, VIB, XVII, XVIII, XXIII, XXVIII, and XXXII) showed neither amide nor carboxylate ion absorption bands. Absorption bands at 5.77 p were correlated with the presence in the polysaccharides of 0-acetyl functions. With few exceptions, the presence of amide and carboxylic acid groups has been confirmed by chemical evidence (see Table II). 

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